Electrical apparatus



Dec. 28, 1954 M, GRAHAM ETAL 2,698,402

ELECTRICAL APPARATUS Filed Sept. 30, 1953 INVENTORS.

JAMES M. GRAHAM LOUIS H SEGALL ATTOR EYS.

United States Patent "'0 2,698,402 ELECTRICAL APPARATUS James M. Graham and Louis H. Segall, Sidney, N. assignors to Bendix Aviation Corporation, New York,

N. 33., a corporation of Deiaware Appiication September 30, 1953; Serial'No'. 383,844

Claims.- (Cl. 315-36) vide a simple and compact structure embodying a plurality of spark -gaps which are electrically associated with each other and novelly disposed with relation to each other.

Another object of the invention is to provide a novelly constructed device of the above character for controlling the flow of electrical energy from a source, such as a charged condenser, to a load, such as the spark gap of an igniter plug of an engine ignition system.

A further object is to provide a novel three-electrode gap construction for an electrical circuit.

The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of Jae invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

Fig. 1 is a side elevation view, partly insection, showing one form of spark gap device embodying the present' invention;

Fig. 2 is a diagrammatic view of one form of electrical circuit in which the device of Fig. l is adapted for use; and

Fig. 3 is a detail View of a terminal.

The single embodiment of the invention illustrated by way of example in the accompanying drawings is in a form which has been successfully employed in ignition systems for gas turbine or jet-type engines. structures embodying the invention are not limited to such use, but may be used in other environments including ignition systems for reciprocating engines, oil burners, and other circuits wherein it is desired to exercise control over the flow of electrical current. shown, the invention comprises a hollow casing 10 of insulating material, the interior of which is designed to receive a pair of spark gap assemblies in a novel manner to provide suitable connections therebetween, and for easy removal thereof for inspection, adjustment, repair, and replacement. Casing 10 may be molded and has an open upper end, a partially closed lower end to provide an opening 11, and an opening 12 in a side wall thereof. The interior of casing 10 comprises a small bore portion 14 at one end, an intermediate medium bore portion 15, a larger bore 16 at the open end, and two annular upwardly facing shoulders and 21.

To provide an electrical terminal at the lower end of casing 10, a flanged eyelet or hollow rivet 17 is seated in the bottom of the casing and extended through opening 11. The outer end of the eyelet is spun over to secure in place a terminal strip 18. Solder may also be used to insure good mechanical and electrical connections between parts 17 and 18. For a purpose to more fully appear hereinafter, a metallic ring or adapter 19 is molded into or otherwise suitably secured within the bore 16 of the casing. Ring 19 is internally threaded at 22 and has an internal flange 23 seated on shoulder 21. A terminal strip 24 may be secured to ring 19 by solder and/or spinning the end of the ring over a portion of the strip surrounding it.

However, ..-1

In the form ICC Slidably and loosely mounted in small bore portion-114 is a sealed sparkgap. device 30 which may be called a control gap. In the form shown, byway of example, said control gap comprises two spacedelectrodes 25iand 26 supported by metallic end plates 27. and 28, .which are secured to the ends of a glass cylinder 29 in any known manner, such as by means of a Kovar glass-to-metal to thereby provide a hermetically sealed spacefor the electrodes. Said space may. be Wholly'or partially evacuated and, if desired, a desirable gaseousmedium may be injected therein to a desired pressureithr'ough. a tube33 which is thensealed. Spark. gap .device .30. may thus beconstructed to insure. breakdown at a substantiaily fixed or predetermined voltage irrespective ofcthe surrounding atmospheric conditions. The end'plat'es .27 and 28 serve as terminals for. the electrodes. ..Arcoil spring 31 may be interposed under compressionbetween gap device 3i) and. the flange of eyelet 17 .to maketelectrical connection between the latter and to urge the upper terminal of device 39 into electrical engagement with another spark gap assembly to be next described.

Removably mounted in the upper and central .bore portions of casing 10 is a novel three-electrodetype spark gap'device 32 which is electrically connected by direct contact with spark gap device 3%. As illustrated inrhe drawing, said novel spark gapdevice comprises a perforated plate or spider33 which is externally threaded to engage threads 22in ring 19, and provided With a central threaded opening to receive the threaded spindle 3'-f.of an electrode 35. The latter is thus mountedfor easy adjustment in the direction of the axis thereof.

Cemented or otherwise'secured to the under or inner surface of spider 33 and extending into casing 11 is a tube of glass or otherv suitable insulating materiak. .A second electrode 37 is suitably. spaced from,;electrode 35, said second elecctrode being annular and having a flange .38 cemented or otherwise suitably secured. tofthe other end of tube 36. Centrally positioned within an annular electrode 37 by a tubular insulator 39 is .a third electrode comprising an enlarged head portion 46 anda spindle 41. if desired, electrode 35 may .have the lower face thereof counterbored to provide a recess opposite electrode 4% or the margin thereof can be faced,- as illustrated, with a ring 51 of tungsten .or like material having high resistance to wearby electrical sparks; The upper surface of electrode 37 may also be facedwith a ring 52 of tungsten, or other material whichresists wear and deterioration from electrical sparking. Rings 51 and 52 may be silver soldered or otherwise suitably secured to the faces of electrodes 35 and 37.

Insulator 39 may be made of glass, or any other 'suitable insulating material. In one suitable embodiment, glass powder is heated to a plastic or molten consistency and pressed into the cavity between electrodes 37- and 4t), 41. When the glass cools, it is effective to hold the parts in assembled relation. The circular end face of electrode head 40 is preferably but not necessarily flush with the end face of annular electrode 37, 52 adjacent electrode 35, 51, and the outer periphery of head 40 is spaced from the inner periphery of electrode..37, 52 to provide a uniform annular gap therebetween. This annular gap, or space, is preferably filled by an end portion of insulator 39 of reduced Wall thickness. As shown, the end face 42 of the insulator is likewise flush with the faces of electrodes 40 and 37, 52, so that the inner and outer peripheries of said surfaces, respectively, are bridged by the face 42.

The assembly comprising center electrode 40, 41 and insulator 39 may include an insulating disk or washer 43 which surrounds spindle 41 and engages the inner marginal portion of the lower face of electrode 37, 38 and a metallic disk or bushing 44 which surrounds and is se-- cured to the extended end of the spindle, such as by soldering. Bushing 44 serves as an electrical contact:

If desired, either or both of the electrodes 37 and 40 may extend a short distance be- Thus, electrodes.

and'holds washems'in place to insulate spindle 41 from adjacent parts of electrode 37,38.-- a e The diameter or transverse dimension of bushing 44 is preferably such that the same will be engaged by the annular surface .45 of end plate 27 under the action of spring 31. The outer margin of the lower face of flange 38. preferably rests on the ring portion of a terminal member 46 (Fig. 3) which in turn rests on shoulder 20, and extends through opening 12 in the side wall of casing 10. Terminal 46 may be secured to flange 38,

if desired.

is less than the source voltage but greater than the breakdown voltage of control gap device 30.

' One suitable circuit wherein the above-described device may be advantageously employed is illustrated diagrammatically in Fig. 2 from which it will be seen that when a relatively high capacity condenser 47 is charged .step by step through a rectifying means 43 or in some other manner to a voltage sufiicient to bridge or jump across the gap between electrodes 25 and 26 of control gap device 30, but insufiicient to bridge the gaps between electrodes 35 and 37 and electrodes 37 and 40, there will be a partial discharge of condenser 47 into a condenser 49 of relatively small capacity. This discharge passes initially through the semi-conductive or highly resistive surface 42 of insulator 39. This initial flow is believed to ionize the air between electrodes 37 and 40, thereby reducing the resistance so that the remainder of the partial discharge may pass through space between the two last-named electrodes from condenser 47 into condenser 49. The gaseous medium between electrodes 37 and 35 is believed to be ionized by this partial discharge and, hence, the resistance is thereby so reduced that the theretofore insufficient voltage across condenser 47 becomes sufficient to bridge said gap, and to permit the 1 remainder of the charge on condenser 47 to flow to an igniter gap or spark plug 50 or other load. An igniter gap of the so-called shunted surface gap type is illustrated at 50, but a conventional spark gap may be used if the source of voltage is sufiicient.

Although only a single embodiment of the invention is illustrated in the accompanying drawings and described in the foregoing specification, it is to be expressly understood that the invention is not limited thereto. For

example, changes may be made in the specific construct tion of spark gap device 30 and equivalent 'or comparable materials may be used for those herein suggested. Various changes may also be made in the specific design and arrangement of the parts illustrated without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. Electrical apparatus of the class described comprising a hollow casing of insulating material, said casing having an internal shoulder intermediate the ends there of,--a terminal member-seated on saidshoulder and extending through an opening in the wall of said casing, a three-electrode spark gap assembly supported on and having one electrode thereof in engagement with said terminal member, a terminal at the end of said casing remote from said assembly, a two-electrode spark gap device in the casing between said terminal and assembly, and resilient means interposed between said spark gap device and said terminal for electrically connecting the same "and urging said device into electrical contact with a second electrode of said assembly.

2. Electrical apparatus as defined in claim 1 wherein the third electrode of said assembly is adjustably mounted in spark gap relation with said one electrode.

3. Electrical apparatus as defined in claim 1 comprising a metallic sleeve secured in said .casing, said assembly and sleeve having cooperating screw threads whereby said assembly is secured in the casing.

4. Electrical apparatus as defined in claim 1 wherein said one electrode and said second electrode are maintained in spark gap relation by insulating means, a sur: face of the latter bridging the spark gap between said electrodes and being semi-conductive.

5. A spark gap assembly comprising a tubular electrode, a center electrode centrally disposed in said tubular electrode, insulating means interposed between said electrodes and bridging the annular spark gap at the end faces thereof, a third electrode, a support for said third electrode, and a cylinder of insulating material secured to and spacing said support and said tubular electrode, whereby said third electrode is supported in spark gap relation to the end face of said tubular electrode adjacent said first-named spark gap.

. 6. A spark gap assembly as defined in claim 5 wherein said third electrode is adjustably mounted in said support.

7. A spark gap assembly as defined in claim 5 wherein said third electrode and said support have cooperating screw threads whereby the spark gap between said tubular electrode and said third electrode may be adjusted.

8. A spark gap assembly as defined in claim 5 wherein said insulating means constitutes the sole mechanical con nection between said tubular electrode and said center electrode.

9. Electrical apparatus of the class described comprising a hollow casing, a terminal at one end of the casing, resilient means contacting said terminal, a sealed spark gap device removably supported in one end of the casing by said resilient means and having an electrode thereof electrically connected to said terminal by said resilient means, and a three-electrode spark gap assembly removably secured in the other end of said casing, the center electrode of said assembly being engaged by the other terminal of said spark gap device under the pressure of said resilient means.

10. Electrical apparatus of the class described comprising a hollow casing, a three-electrode spark gap assembly mounted in one end of said casing, a two-electrode spark gap device in the other end of said casing, and resilient means supporting said device and urging one terminal thereof into engagement with an electrode of said assembly.

No references cited. 

